type Lens s t a b =
  forall f. Functor f =>
    (a -> f b) -> s -> f t

_1 :: Lens (a, c) (b, c) a b
_1 = _

_2 :: Lens (c, a) (c, b) a b
_2 = _

Gaining an understanding of the Lens type has been on my todo list for a long time. So I finally bit the bullet and read up a little. These are (more or less) my notes as I went along.

I sought to understand what the fuss was all about and I’ve now added to the mass of Monad Explainer posts on the internet.

readAFile().then(function (content) {
  return writeAFile(content)
}).then(function (report) {
  console.log(report)
})